1. Field of the Invention
This invention relates to missile defense systems, and in particular, but not exclusively, to a system for intercepting and destroying exo-atmospheric missiles using kinetic energy kill vehicles.
2. Description of the Related Art
Ballistic missiles armed with conventional explosives, chemical, biological or nuclear warheads represent a real and growing threat to the United States from the former Soviet Union, terrorist states and terrorist groups. The technologies required to both create weapons of mass destruction (WMD) and to deliver them over hundreds to thousands of miles are available and being aggressively sought by enemies of the United States.
Several modern missile defense systems are under development by branches of the US Armed Services and Department of Defense. These systems use an (interceptor) missile to destroy an incoming (target) missile, warhead, reentry vehicle, etc. . . . Blast-fragmentation systems detonate high power explosives shortly before the collision of the interceptor with the target. Kinetic energy systems rely solely on the kinetic energy of the interceptor to destroy the target. Both systems require highly sophisticated guidance systems to acquire and track the target. In particular, kinetic energy systems must hit the target with great precision.
U.S. Pat. Nos. 4,738,411 and 4,796,834 to Ahlstrom describe techniques for guiding explosive projectiles toward the target. In the '411 patent, the magazine is loaded with transmitting projectiles with means for illuminating the target with electromagnetic radiation and explosive projectiles with a passive or purely receiving homing device. During the last part of its travel, the transmitting projectile illuminates the target area with electromagnetic energy. A preferred wavelength range is the so called millimeter wavelength range, suitably 3-8 mm. Energy reflected off of any targets within the target area is received by the explosive projectiles and used to guide the projectiles toward the target. A leading projectile passively detects and then illuminates a target. A trailing projectile detects the return energy off of the illuminated target and corrects its trajectory accordingly. When the leading projectile hits the ground, the trailing projectile senses the interruption and resets itself to passive detection. When the target's own radiation is detected, the passive signature is used for final guidance. The detector device for activating the illumination source is preferably the same detector as that included in the target tracking device.
Raytheon has fielded a unitary Kill Vehicle system that represents state-of-the-art in kinetic energy systems designed to locate, track and collide with a ballistic missile. The unitary interceptor includes a single kill vehicle (KV). The interceptor is launched on a multi-stage rocket booster. Current versions of the kill vehicle have large aperture optical sensors to support the endgame functions including: acquisition of the target complex, resolution of the objects, tracking the credible objects, discrimination of the target objects and homing in on the target warhead.
The deployment of missiles with Multiple Independently Targeted Re-entry Vehicles (MIRVs) and advanced decoys is driving a move to develop interceptors that can deploy multiple kill vehicles. A multiple kill vehicle (MKV) interceptor would include a carrier vehicle (CV) and multiple KVs. There is a strong desire to use the existing base of booster stages to deploy the MKVs and to maintain compatibility with existing command, control, and communication infrastructure and Built-in Test (BIT) procedures. The development of an MKV interceptor presents unique problems of weight, miniaturization, and control bandwidth to acquire, track and intercept multiple targets in addition to all the issues encountered by unitary interceptors. Consequently, an effective MKV interceptor has not yet been developed or deployed.
One concept being pursued is to simply miniaturize existing unitary interceptors. In this approach, each KV includes all of the intelligence needed to discriminate targets and provide guidance to impact. The CV is merely a bus to transport the KVs from launch to release. Unfortunately, the ability to “miniaturize” all the functionality into a small, lightweight KV is well beyond state-of-the-art and may never be realizable due to fundamental physics constraints. For example, the bi-directional space-to-ground data link is dictated by the distance between the KV and the ground station, the ability of the sensor to have adequate detection range and resolution is proportional to the aperture size, and the Focal Plane Assembly (FPA) cryo cooling system is relatively fixed. The mass/power/volume requirements of these crucial subsystems cannot simply be made smaller without a substantial performance penalty.
Another concept is to “command guide” all of the KVs from the CV to impact. In this approach all of the intelligence needed to discriminate targets and provide guidance to impact is located on the CV. The KVs include minimal functionality, typically only a receiver and actuators to respond to the heading commands sent by the CV. U.S. Pat. No. 4,925,129 describes a missile defense system including a guided projectile with multiple sub-projectiles. A radar tracker is used to guide the projectile toward a target at relatively large distances. An optical tracker on the projectile is used to track the target at relatively small distances and issue guidance commands to guide the sub-projectiles to intercept the target. Although conceptually attractive, command guidance suffers from poor target resolution and latency associated with the stand-off range of the CV to keep all targets within the optical tracker's field of regard. Furthermore, the CV must have sufficient bandwidth to track all of the targets simultaneously.